1. Field of the Invention
The present invention relates to an image reading apparatus incorporated in a facsimile machine, a scanner and the like.
2. Description of the Related Art
As is well known, a conventional image reading apparatus includes a light source for irradiating a document brought to an image reading section, and a plurality of light receiving elements mounted on a printed circuit board. The light receiving elements are arranged to receive light reflected at the image reading section and output image signals (which are relatively weak) in accordance with the received light. These image signals are sent to a predetermined position via a wiring pattern formed on the printed circuit board. The light source and the printed circuit board are accommodated in a suitable container.
The conventional image reading apparatus have been found disadvantageous in the following points.
It is assumed that a cold-cathode tube is used for the light source of the image reading apparatus. For actuating the cold-cathode tube, high-voltage and high-frequency driving power needs to be supplied to the cold-cathode tube. To this end, typically, use is made of an inverter connected to the cold-cathode tube via a connection cable.
In the above arrangement, due to the use of the high-voltage and high-frequency driving power, electrical noises may be generated at the inverter or the connection cable or the cold-cathode tube. The occurrence of electrical noises is unfavorable since the electrical noises tend to adversely influence the relatively weak image signals supplied by the light receiving elements.
The above problem may seem to be solved by using a light-emitting diode (which does not need high-voltage and high-frequency driving power) for the light source instead of the cold-cathode tube. However, when the image reading apparatus is incorporated in e.g. a facsimile machine, electrical noises may well be generated at some of the components or elements contained in the facsimile machine.
Turning back to an instance where a cold-cathode tube is used for the light source, the conventional image reading apparatus also suffers from the following problem.
As shown in FIG. 22 of the accompanying drawings, a conventional cold-cathode tube has an elongated, straight configuration. Specifically, the conventional cold-cathode tube has two longitudinal ends 39 and an intermediate portion 3e located between the ends 39. As illustrated, the cold-cathode tube has a length which is generally equal to the width L1 of a document 90 to be read out. Such an arrangement has the following disadvantage.
Reference is now made to FIG. 23 which shows the relationship between relative luminosity of the conventional cold-cathode tube and longitudinal positions of the cold-cathode tube. As can be seen, the relative luminosity at the ends 39 of the cold-cathode tube (indicated by reference character C) is unduly smaller by about 20-30% than that in the intermediate portion 3e. Thus, when the length of the cold-cathode tube is equal to the width L1 of the document (FIG. 22), the cold-cathode tube will fail to properly irradiate the end portions of the document corresponding in position to the ends 39 of the cold-cathode tube.
In order to overcome the above problem, an arrangement shown in FIG. 24 may be adopted. According to the illustrated arrangement, the length L2 of the cold-cathode tube is rendered greater than the width L1 of the document 90. In this manner, every portion of the document 90 can be irradiated with an equal amount of light emitted from the intermediate portion of the cold-cathode tube.
However, with the arrangement shown in FIG. 24, the ends 38 of the cold-cathode tube are located outside of the document 90 as viewed in the primary scanning direction. Clearly, this arrangement is disadvantageous since the size of the image reading apparatus is unfavorably made larger due to the increased length of the cold-cathode tube.
Further, a certain amount of light is emitted from the ends 38 of the cold-cathode tube. However, in the arrangement shown in FIG. 24, the light from the ends 38 will simply be wasted without being used to irradiate the document 90.
It is, therefore, an object of the present invention is to provide an image reading apparatus which eliminates or reduces the above-described problems.
According to a first aspect of the present invention, there is provided an image reading apparatus comprising:
a cold-cathode tube for irradiating a linearly extending image reading section, the cold-cathode tube including a first end portion, a second end portion, and an intermediate portion arranged between the first end portion and the second end portion; and
a plurality of light receiving elements for receiving light reflected at the image reading section;
wherein at least one of the first and the second end portions extends in a direction differing from another direction in which the intermediate portion extends.
With such an arrangement, a document to be read out is advantageously irradiated since the first or second end portion extends from the intermediate portion at a certain angle (90 degrees for example). Further, with the above arrangement, the longitudinal dimension of the cold-cathode tube can be reduced. Thus, the image reading apparatus incorporating the cold-cathode tube can be reduced in size.
According to a preferred embodiment, each of the first and the second end portions extends in a direction differing from said another direction.
The image reading apparatus further comprises a lens array for focusing the reflected light onto the light receiving elements, wherein the lens array is disposed in a region defined by the first end portion, the second end portion and the intermediate portion.
With such an arrangement, the lens array and the cold-cathode tube are compactly held in place.
The image reading apparatus may further comprise an inverter for supplying power to the cold-cathode tube, wherein the lens array is disposed between the inverter and the intermediate portion.
According to a second aspect of the present invention, there is provided a cold-cathode tube for irradiating an image reading section of an image reading apparatus comprising:
a first end portion provided with an electrode;
a second end portion provided with another electrode; and
an intermediate portion arranged between the first end portion and the second end portion;
wherein at least one of the first and the second end portions extends in a direction differing from another direction in which the intermediate portion extends.
According to a third aspect of the present invention, there is provided an image reading apparatus comprising:
a light source for irradiating an image reading section;
a plurality of light receiving elements for receiving light reflected at the image reading section;
a printed circuit board having an upper surface for mounting the light receiving elements and a lower surface opposite to the upper surface;
a container for accommodating the light source and the printed circuit board;
an outer shield member which is grounded and externally attached to the container; and
an inner shield member which is accommodated in the container and electrically connected to the outer shield member.
With such an arrangement, electrical noises can be shielded by the outer and the inner shield members, so that the relatively weak image signals supplied from the light receiving elements will not be adversely influenced by the noises.
The light source may comprise a cold-cathode tube, the inner shield member being arranged between the cold-cathode tube and the printed circuit board.
According to a preferred embodiment, the image reading apparatus further comprises a reflector for supporting the cold-cathode tube, wherein the inner shield member defines a groove for accommodating the reflector.
The container may be formed with a first hollow portion for accommodating the inner shield member.
The image reading apparatus may further comprise a light-guiding member for leading light from the light source to the image reading section, and a reflector for supporting the light-guiding member.
The light source may comprise a light-emitting diode mounted on the upper surface of the printed circuit board.
The light-guiding member may include a plurality of side surfaces arranged to totally reflect light propagating through the light-guiding member.
The light-guiding member may also include a light-emitting surface for allowing the propagating light to leave the light-guiding member.
Preferably, the outer shield member is arranged to cover the lower surface of the printed circuit board.
The outer shield member may have an upwardly open, box-like configuration.
The container may be formed with a second hollow portion for accommodating the printed circuit board, the outer shield member being arranged to come into contact with the lower surface of the printed circuit board so that the printed circuit board is kept within the second hollow portion.
The printed circuit board may be provided with an electrode for grounding, the inner shield member being electrically connected to the electrode for grounding, the outer shield member being electrically connected to the inner shield member.
The inner shield member may be formed with a first terminal projecting from the inner shield member, the first terminal being elastically pressed against the electrode for grounding.
The outer shield member may be formed with a second terminal projecting from the outer shield member, the second terminal being elastically pressed against the inner shield member.
The inner shield member may be provided with an auxiliary portion extending externally of the container, the auxiliary portion being held in contact with the outer shield member.
Other objects, features and advantages of the present invention will become clearer from the detailed description of preferred embodiments given below with reference to the accompanying drawings.